System of eliminating the higher harmonic voltage of any alternating current circuit



Nov. 8, 1960 TORAO NAGAI 2,959,738

- SYSTEM OF ELIMINATING THE HIGHER HARMONIC VOLTAGE OF ANY ALTERNATING CURRENT CIRCUIT Filed Jan. 21, 1959 3 Sheets-Sheet 1 Fig 1 Feed Impedance back 7 l am lifter Z P v v 1 AM (I j 2 m e n TransmLssLon O i I i factor In 2- Feed back iransmtssion factor IN V EN T013.

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SYSTEM OF ELIMINATING THE HIGHER HARMONIC VOLTAGE OF ANY ALTERNATING CURRENT CIRCUIT Filed Jan. 21, 1959 3 Sheets-Sheet 2 Fig .3;

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SYSTEM OF ELIMINATING THE HIGHER HARMONIC VOLTAGE OF ANY ALTERNATING CURRENT CIRCUIT Filed Jan. 21, 1959 3 Sheets-Sheet 3 y 4- HM 7711M harmonic resonant element 4K1? Kl Efth harmonic h) Endwnental Hmse Mixing Volume aiteflmuwu P)- v a l D netwarx compensator mp lf r 71th. harmanic resonam element Km L mH 1 I 70 1 60 W (H O I l l IN V EN TOR.

Unite rates atet I SYSTEM OF ELIMINATKNG THE HIGHER HAR- MQNEQ VOLTAGE OF ANY ALTERNATING CUR- RENT (IIRCUIT Torao Nagai, Niigata-shi, Japan, assignor to Agency of Industrial Science and Technology, Ministry of international Trade and Industry, Tokyo-to, Japan, a corporation of Japan Filed Jan. 21, 1959, Ser. No. 788,077

Claims priority, application Japan Feb. 6, 1958 4 Claims. (Cl. 328-167) The present invention relates to an improved system of eliminating the higher harmonic electric voltage of an alternating current circuit.

An object of the present invention is to provide a system capable of stably and surely eliminating the higher harmonic electric voltage occurring between two points of any alternating current circuit.

Said object and other objects of the present invention have been attained by the apparatus which comprises a main resonant branch consisting of parallelly connected resonant branch elements which are, respectively, made to resonate with the harmonics to be eliminated, a harmonic feed back amplifier consisting of a harmonic frequency selective amplifier with parallelly connected resonant ele ments each being made to resonate with respective harmonic to be eliminated and a mixing amplifier totalizing the output of said harmonic frequency selective amplifier, an inductive member which is parallelly connected to said main resonant branch, and a saturated iron core type choke coil which is parallelly connected to the output side of said feed back amplifier, the output of said harmonic feed back amplifier being fed back to the input side of said harmonic feed back amplifier through said main resonant branch and a coupling transformer, the inductance of said inductive member being selected to compensate the fundamental current passing through said main resonant branch and the inductance of said choke coil being selected to eliminate the low frequency oscillation due to the insertion of said inductive memher.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its manner of construction and operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which the same members are indicated by the same references, and in which:

Fig. 1 is a schematic connection circuit diagram for showing the principle of the present invention;

Fig. 2 is a block diagram of the circuit of Fig. 1;

Fig. 3 is a schematic connection circuit diagram of the harmonic frequency selective amplifier of the apparatus of the present invention;

Fig. 4 is a block diagram of the circuit of Fig. 3;

Fig. 5 is a characteristic curve for showingthe relation between the inductance and electric voltage of a choke coil having a saturated iron core.

The principle of the present invention will be first described in connection with the connection circuit diagram of Fig. 1, in which the electric circuit includm an alternating current source S, an impedance 2,, a nonlinear load Z a feed back amplifier AM, a main resonant branch MRB, and a coupling transformer T which couples said amplifier AM with said resonant branch MRB, said amplifier, transformer and resonant branch being so connected that the electric voltage :3 produced in the circuit by the harmonic electric voltage e, included in the alternating current source S or load 2;, may be applied to the input terminals 1 and 2 of the feed back amplifier AM. The feed back amplifier AM consists, as shown in Figs. 3 and 4, of a fundamental voltage attenuation network K :1 phase compensator K for compensating the phase of the feed back voltage, a harmonic frequency selective amplifier K consisting of parallelly connected harmonic frequency selective resonant elements K ,K K which are, respectively, resonatable with the third, fifth, nth harmonic frequencies, and a mixing amplifier K, which amplifies the resultant output power of said resonant elements.

Again, referring to Fig. 1, the output power of said feed back amplifier AM is fed back to the input terminals 1 and 2 thereof through a coupling transformer T, a choke coil L having a saturated iron core and a main resonant branch MRB consisting of a plurality of parallelly connected resonant branch elements which consist, respectively, of an inductance coil L a resistance R and a condenser C an inductance coil L a resistance R and a condenser C said elements being designed, respectively, to be resonated with the third, fifth nth harmonic frequencies.

The distinctive feature of the present invention consists in that the output power of the amplifier AM is so fed back to the input side of said amplifier that the fundamental current passing through the main resonant branch MRB may be suppressed by an inductance coil L connected in parallel to said branch MRB as well as the low frequency oscillation due to the connection of said inductance coil L may be suppressed by a choke coil L connected to the secondary circuit of the coupling transformer T.

The operation of the present invention will be described as follows in connection with Fig. 1. First, we describe in connection with the case in which the load Z is disregarded. Now, when it is assumed that the fundamental voltage of the electric source S, the nth higher harmonic voltage of said source S and the remaining nth higher harmonic voltage between the connection lines in, and m are, respectively, represented by E e, and c the relation between said voltages e, and e is represented by the following Equation 1 when the inductance coil L and the choke coil L are disregarded.

in which K ,K ,K and K represent, respectively, feed back transmission factors of the members K ,K ,K and K and Z represents the impedance of the resonant branch element consisting of the inductance coil L resistance R and condenser C said impedance becoming equal to R when said element is resonated.

Now, when we adopt the condition represented by the following Equation 2, the Equation 1 is transformed into the Equation 3 in which K represents the transmission factor due to the impedances Z and Z,,.

It? 1+1? KiKtKiKt In the Equation 3, the ratio becomes very small, when the factor K K K K K is selected to be suitably large. This case is equivalent to the case in which the higher harmonic voltage e is removed by shortcircuiting thereof. The Equation 3 can be represented by the block diagram of Fig. 2, in which the factor K K K K and the factor K represent, respectively, the feed back transmission factor of the feed back amplifier AM and the transmission factor due to the impedances Z and Z For stabilizing the condition of the Equation 3, it is necessary that the pole of the denominator gives attenuation at the transient period, that is to say, the phase angle of the factor K K K K K is always within 180. This object can be attained by connecting the harmonic frequency selective resonant elements K K K in parallel as shown in Fig. 3, that is to say, by applying the output power of the phase compensator K to the parallelly connected vacuum tubes V V V of the harmonic frequency selective resonant elements K K K through the terminals 5 and 6. Now, speaking in connection with the third harmonic frequency selective resonant element K the harmonic voltage between the terminals 5 and 6 applied to the vacuum tube V at its grid circuit is suitably amplified by the plate resistance R This amplified voltage is applied to the grid circuit of the vacuum tube V The plate current of the vacuum tube V is amplified by cathode fall at the resistance R and then is applied to a twin-T network B consisting of a third harmonic resonant circuit through a condenser C thereby the other harmonic voltages except the third one are removed by the vacuum tube V and only the desirable third har monic voltage is obtained at the resistance R This voltage of the resistance R is applied to the grid circuit of the vacuum tube V of the mixing amplifier K Similarly, the other harmonic voltages such as fifth, seventh, nth haromonic voltages are, respectively, applied to the grid circuits of the other vacuum tubes V V V of the mixing amplifier K thus producing the corresponding harmonic anode voltages in said vacuum tubes. 'Ihese harmonic anode voltages are mixed in parallel and then amplified through a power amplifier AMP. This amplified voltage is led out as a feed back harmonic voltage K K K K e through the coupling transformer T.

Now, let it be described in connection with the case, in which the fundamental voltages having the frequencies between 45 c./s. and 55 c./s. are to be suppressed and the other harmonic voltages are to be amplified. In such a case, the amplifier of stagger connection type is used to reduce the gain of the fundamental voltage as much as possible in comparison with that of the higher harmonic voltages. For example, the amplifying elements for suppressing, respectively, the voltages of the frequencies 45, 48, 51 and 55 c./s. to be suppressed are connected in series with one another. According to this connection, the gains of the fundamental and harmonic voltages become, respectively, about 10- and 10- order. Accordingly, an extraordinarily large effect for eliminating the fundamental voltage will be obtained. However, since the phase angles of the above-mentioned gains obtained in the frequency range of 0 c./s. vary over the wide range of -350-0-+350, the stable condition as shown in the Equation 3 cannot be obtained.

However, when the frequency selective resonant elements K K K are connected in parallel as shown in Fig. 3, the phase angles can be set within :180.

Now, when the feed back harmonic voltage K K K K e is fed back to the input terminals 1 and 2 of the feed back amplifier AM through the main resonant branch MRB as shown in Fig. 1, fundamental leading currents passing, respectively, through the resonant elements of said branch MRB, said currents being, respectively, proportional to the capacities of the condensers C C C,,, are produced by the fundamental voltage E of 4 the electric source S. In this case, if the inductance coil L and choke coil L are disregarded, the resultant current of said leading currents passing through said resonant elements passes through the secondary coil of the coupling transformer T, thus causing impossibility of the operation of the mixing amplifier K in Figs. 3 and 4.

However, according to the present invention, since the inductance coil L is parallelly connected to the main resonant branch MRB, passing of the fundamental leading current into the transformer T can be effectively suppressed by designing said inductance coil L as to produce a lagging current having the amplitude equal to that of the resultant leading current of said branch MRB and having the phase opposite to that of said resultant leading current.

However, there is an apprehension in that when said inductance coil L is used, the low frequency parts of the transmission factor K K K K K are increased and their phases approach to 180. This disadvantage can be eliminated by parallelly connecting a saturated iron core type choke coil L to the output terminals 3 and 4 of the coupling transformer T. The characteristic curves between the inductance of the choke coil L and the voltage V thereof are shown in Fig. 5, in which the curve II was obtained by actual experiment in connection with the case of .the frequency (f=l50 c./s.). The permeability of the choke coil L may be regarded to be always equal for the other frequencies except c./s. so far as the current passing through said choke coil is always the same. Accordingly, the characteristic curve I in the case of the frequency (f=1.5 c./s.) can be obtained from the curve II by shifting the curve H leftward by of the graduation of the voltage V Similarly, the characteristic curve III in the case of the frequency (f=550 c./s.) can be obtained from the curve II by shifting the curve II rightward by of the graduation of the voltage V When an oscillation voltage V of about 0.01 v. and of low frequency 1.5 c./s. appears, the amplitude of this voltage increase gradually, but the inductance of the choke coil L decreases suddenly upon the increase of said voltage over 0.1 v., whereby the oscillation voltage V is almost shortcircuited by the choke coil L when said voltage exceeds 0.2 v. Accordingly, the oscillation voltage V is not fed back through the inductance coil L thus eliminating the oscillation. On the contrary, when any higher harmonic voltage (V =1-10 v.) to be selected and having a frequency between 150 and 550 c./s. appears at the output terminals 3 and "4- of the transformer T, the inductance of the choke coil L becomes 50 mH and the reactance thereof becomes over 509 for said frequency. Since said reactance corresponds to a value over about ten times the resonant impedance of the resonant branch MRB, the selected harmonic output of the transformer T passes mainly through the main resonant branch MRB without passing through the choke coil L As a whole, according to the present invention, in the system wherein a harmonic feedback amplifier comprises a harmonic frequency selective amplifier consisting of parallelly connected harmonic resonant elements each be ing made to resonate with respective harmonic voltage to be eliminated and comprises a mixing amplifier leading out the resultant output of said selective amplifier through a main resonant branch and the output voltage of the feedback amplifier is fed back to the input side of the feed back amplifier, the fundamental current flowing through said main resonant branch is compensated by an inductance coil connected parallel'ly to said main resonant branch and the dangerous low frequency oscillation due to the existance of said inductance coil is removed by a saturated iron core type choke coil connected to the secondary side of the output transformer, whereby the higher harmonic voltage appearing between two points in an alternating current circuit can be stably and surely removed. Accordingly, the present invention is very effective for any precise electrical measuring apparatus which necessitates an electric voltage of purely sine wave.

What I claim is:

1. In an apparatus for the elimination of higher harmonic voltage of an alternating current circuit of the type comprising a main resonant branch to resonate with the harmonic to be suppressed, a harmonic feedback amplifier consisting of a harmonic frequency selective amplifier and a mixing amplifier totalizing the output of said selective amplifier, said selective amplifier being composed of parallelly connected resonant elements, each of said elements being able to resonate with respective harmonic to be suppressed, the output of said harmonic feedback amplifier being fed back to the input side of said feedback amplifier through said main resonant branch; that improvement wherein an inductive member is inserted in parallel in said main resonant branch and a saturated iron core type choke coil is inserted in the output side of said feed back amplifier, the inductance of said inductive member being selected to compensate the fundamental current passing through said main resonant branch and the inductance of said choke coil being selected to eliminate the low frequency oscillation due to the insertion of said inductive member.

2. An apparatus for the elimination of higher harmonic voltage of an alternating current circuit as claimed in claim 1, in which the main resonant branch consists of parallelly connected resonant branch elements which are, respectively, made to resonate with the harmonics to be eliminated, an inductance coil is used as the inductive member, and a coupling transformer is connected to the output side of the harmonic feed back amplifier, the saturated iron core type choke coil being connected in parallel to the secondary side of said coupling transformer and the output of said amplifier being fed back to the input side of said amplifier through the main resonant branch and said coupling transformer.

3. An A.C. circuit to eliminate the higher harmonic frequency voltages of a fundamental frequency voltage comprising a feedback amplifier connected across the voltage source, a transformer having its primary connected to the output of said amplifier, a series circuit comprising a main resonant branch and a choke coil connected across the said amplifier input terminals, the secondary of said transformer connected across the said choke coil, and an inductor connected in parallel with the said main resonant branch to suppress the fundamental frequency voltage therein said choke coil having such an inductance as to suppress the oscillations generated by the connection of said inductor in the circuit.

4. The invention as set forth in claim 3 wherein the said feedback amplifier comprises a plurality of parallel connected harmonic frequency selective resonant circuits each resonating at a respective harmonic frequency, and a mixing circuit connected to the last recited circuits to amplify the resultant output.

Scott Sept. 19, 1939 Rust et a1. Apr. 7, ,1942 

